One-Rep Max Calculator

The five formulas — how they differ

Epley (1985): 1RM = w × (1 + r/30). The most widely-used; biased slightly high in the 1–3 rep range, accurate in the middle. Mayhew 1995 found Epley most accurate for bench press.

Brzycki (1993): 1RM = w × 36 / (37 − r). Conservative at low reps, slightly high at 8+ reps. Often cited as the most accurate overall single formula in subsequent validation studies.

Lombardi (1989): 1RM = w × r^0.10. The most conservative of the common formulas; underestimates 1RM by a couple of % vs the others. Good choice for safety-first programming.

Lander (1985): 1RM = (100 × w) / (101.3 − 2.67123 × r). Similar to Brzycki at low-mid reps; diverges at very high reps.

O\'Conner (1989): 1RM = w × (1 + 0.025 × r). The most conservative across all rep ranges; useful as a "floor" estimate.

Reps-to-percent reference table

The classic Prilepin-influenced table for estimating 1RM from any rep count:

• 1 rep = 100% of 1RM
• 2 reps = ~95% of 1RM
• 3 reps = ~93% of 1RM
• 5 reps = ~87% of 1RM
• 8 reps = ~80% of 1RM
• 10 reps = ~75% of 1RM
• 12 reps = ~70% of 1RM
• 15 reps = ~65% of 1RM
• 20 reps = ~60% of 1RM

How to use the percentage table for programming

Most barbell strength programs prescribe load as a percentage of 1RM:

• 5/3/1 (Wendler): works at 65–95% of "training max" (90% of 1RM)
• Starting Strength linear progression: all working sets are 85–95% effort, increment by 2.5–5 kg per session
• Sheiko (Russian): 50–85% for high-volume technique work, occasional 90%+ singles
• Smolov base mesocycle: 70–85% across the cycle, increasing load each microcycle
• Conjugate (Westside): max-effort day at 90%+, dynamic-effort day at 50–60% with speed

For any of these, plug your real 5RM or 3RM into this calculator, take the estimated 1RM, and apply the program\'s percentage prescription. Most programs round down to the nearest 2.5 or 5 lbs.

Real 1RM testing vs estimating

Real one-rep max testing has a place — but it\'s narrower than most lifters think. It genuinely matters for: powerlifting meet prep, percentage-precise programs that mandate retest cycles, and athletes whose sport requires neural drive at high loads (Olympic weightlifting, strongman). For everyone else — recreational lifters, hypertrophy-focused training, general strength — periodic 3RM or 5RM tests provide more reliable strength trajectory data with much lower injury risk. The Greg Nuckols / Stronger By Science consensus is that under-10-rep estimated 1RM is the practical standard for non-competitors, and explicit max attempts should be saved for situations where the precision matters.

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Frequently asked questions

How accurate are 1RM estimation formulas?

For trained lifters working at 2–6 reps, modern formulas (Epley, Brzycki, Lombardi) predict actual 1RM within 3–8% in most subjects. Mayhew 1995 (Journal of Strength and Conditioning Research) compared multiple formulas against measured 1RM in 440 college athletes and found Epley most accurate for bench press, Brzycki most accurate for upper-body exercises in general, and all formulas degraded sharply above 10 reps. The error increases for beginners (less consistent rep speed), powerlifters peaking for competition (singles are highly individual), and exercises where technique fails before muscle does (squat, deadlift).

Which formula should I trust?

Use the average of multiple formulas — the calculator does this automatically. For programming purposes, the difference between Epley's prediction and Brzycki's prediction at 5 reps is typically 1–2%, which is well within day-to-day strength variation anyway. If you have to pick one: Epley is the most widely-used and works well across rep ranges. Brzycki is slightly more accurate for very low reps (2–3). Lombardi is the most conservative and best for safety-first programming.

Why does the 1RM matter if I don't compete in powerlifting?

Two practical reasons. First, structured strength programs (5/3/1, Starting Strength, Sheiko, Conjugate, Texas Method) prescribe load as a percentage of 1RM. Knowing your estimated 1RM lets you follow the program without re-testing every cycle. Second, 1RM is the most precise single marker of strength progression — much more sensitive than rep PRs for tracking long-term gains. Even if you never lift a true single, periodic 3RM or 5RM tests + 1RM estimates give a clean strength trajectory.

Should I actually test my real 1RM, or just estimate?

For powerlifters and competitive athletes: yes, real singles are necessary for peaking and competition prep. For everyone else: rarely. Real 1RM testing is high-injury-risk relative to the information value, requires deload before and after, and produces a single data point that depreciates quickly. The Strongest 5RM or 3RM test you can repeat every 8–12 weeks gives far more useful data than occasional 1RM tests. Most online lifting communities (r/weightroom, Stronger By Science) recommend estimated 1RM via 3RM or 5RM as the practical standard for non-competitors.

Why do my squat and bench have different 1RM curves?

Different exercises have different rep-to-1RM relationships. Squat and deadlift tend to have steeper drop-offs at higher reps because they're more cardiovascularly demanding — a 10RM squat is closer to ~70% of 1RM, while a 10RM bench press is closer to ~75%. Olympic lifts (snatch, clean & jerk) are extreme — most lifters can only do 3–5 reps at 80% of 1RM due to technique demands. The formulas in this calculator are tuned for the "big three" powerlifts and overestimate Olympic lift 1RMs.